The present invention relates generally to coating processes, and more particularly to such processes used for fabricating targets.
The attainment of lasing action at shorter and shorter wavelengths has been an on-going field of research with many articipated applications.
The traditional laser consists of an active medium pumped in some manner to produce an inverted population between two states, and inserted between mirrors which form an optical resonant cavity. A later discovery showed that intense emission could be obtained from systems without optical cavities. These high-gain mirrorless systems have been appropriately termed amplified spontaneous emission (ASE) systems. ASE systems are of major importance in shortwavelength lasers such as X-ray lasers. To produce gain in ASE systems, high inversion densities are called for and very rapidly rising pump pulses are required to achieve inversion and gain prior to equilibration.
One source given serious consideration for pumping X-ray transitions is laser beams, particularly the very short pulsewidth, mode-locked picosecond beams. By mode-locking, Nd.sup.+3 laser beams can be made to have pulsewidths of 10.sup.-12 seconds and they can be focused to small volumes with high irradiance. However, the photon energy is too small to pump X-ray transitions directly, so the high-power laser pulse must be used to vaporize and heat a pump material to generate plasma X-rays which in turn fall onto a nearby lasing material and optically pump the latter's energy levels to inverted populations.
Because of the importance of gain-per-unit length, the lasing material should have a large length-to-width or aspect ratio. One target configuration satisfying this requirement consists of a stripe of lasing material overcoating a matrix of pump material. Unfortunately, some materials of interest cannot be obtained in this geometry by conventional means such as evaporating, milling, coating, etc. because of their high vapor pressure. A specific example is the neon-sodium system in which the Na X 1s.sup.2 -1s 2p.sup.1 P line at 11.00 Angstroms is used to optically pump the Ne IX 1s-1s 4p.sup.1 P line at 11.001 Angstroms creating an inversion primarily in the n=3 and n=2 levels of Ne IX, and a stimulated emission at 82 Angstroms. Because of the noble gas behavior of neon, it cannot be fabricated by known methods, into the above geometry for lasing action to take place.